Recent research in the area of infant mental health has consistently found that children who experience difficulties in the regulation of emotion are more likely to experience problems in social relationships and thus, are more prone to the development of psychopathology. However, many questions remain concerning the mechanisms, especially biological and caregiver influences that may be implicated in the development of adaptive versus maladaptive emotion regulation. The proposed longitudinal study is guided by a multi-level model of development of emotion regulation that incorporates both intrinsic (biological) and extrinsic (caregiver) influences and hypothesizes that these factors interact to predict both infant emotion regulation and subsequent socioemotional functioning. Thus, the specific goal of this proposal is to examine relations among physiological and emotion regulation in infants, physiological regulation and early attachment behaviors in mothers, and attachment security in mother-infant dyads. Bidirectional and dynamic interactions between mothers and infants will be investigated at 3, 6, and 12- months of age during challenging social situations. The study will yield important information on the complex transactions between infants and caregivers across the first year of life, with the long-term goal of identifying specific behaviors that could be targeted in an intervention program for mothers with high-risk infants.